As shown in, for example, Japanese Laid-Open Patent Application No. 9-173360, a power toothbrush, which can perform reciprocal linear driving in axial direction of a shaft and reciprocal rotation driving (rolling driving) around the axis selectively with using mechanical driving conversion mechanism, is known. In this power toothbrush, it is possible selectively to perform two motions of the reciprocal linear driving in the axial direction of the shaft and the rolling driving around the axis of the brush body attached to the shaft via the driving conversion mechanism by switching rotation direction of a motor.
In such a power toothbrush utilizing the mechanical driving conversion mechanism, a configuration of the driving conversion mechanism for switching between the reciprocal linear driving in the axial direction of the shaft and the rolling driving around the axis becomes complex. According to this, the power toothbrush becomes upsizing, and assembly of it becomes difficult causing the increase of the cost.
On the other hand, for example, Japanese Laid-Open Patent Publication No. 2002-176758 shows a power toothbrush which reciprocally and linearly drives a brush body attached on a shaft in axial direction of the shaft with using a reciprocation type linear driving actuator. This reciprocation type linear driving actuator can perform only the reciprocal linear driving of the shaft, but cannot perform the rolling driving. It, however, is described as a reference of the conventional actuator using permanent magnets and coil.
This conventional actuator is described with reference to FIG. 16. With this conventional reciprocation type linear driving actuator 150, a plunger 151 formed of a magnetic material is fixed on an outer periphery of a shaft 152. The shaft 152 is pivoted by a bearing 162 capable of reciprocally and linearly moving in a direction (axial direction) parallel to the center axis thereof. A ring shaped coil 154 is disposed on an inner peripheral surface of a shielding case 153 with a predetermined clearance with respect to the outer periphery of the plunger 151. Furthermore, ring shaped permanent magnets 155 and 156 which are magnetized in symmetrical with respect to the coil 154 are disposed on the inner peripheral surface of the shielding case 153 and on both sides of the coil 154 in the above axial direction. Ring shaped first yokes 157 and 158 are respectively disposed between the permanent magnets 155 and 156 and the coil 154, and ring shaped second yokes 159 and 160 are disposed at positions opposite to the permanent magnets 155 and 156 with respect to the coil 154. A spring member 161 is disposed between the plunger 151 and the shielding case 152 (SIC: correctly 153) for applying an accompanying force to the plunger 151 in a one direction among the reciprocation directions of linear driving. Then, by supplying an alternating current to the coil 154, the plunger 151 can be reciprocally and linearly driven in the axial direction.
However, in the above-mentioned reciprocation type linear drive actuator 150 using the conventional permanent magnets and the coil, the permanent magnets 155 and 156 are disposed with the clearance with respect to the outer periphery of the plunger, so that inside diameter and outside diameter of the ring shaped permanent magnets 155 and 156 become larger, and volumes of the permanent magnets 155 and 156 also become larger. Following to this, the cost of the permanent magnets 155 and 156 in material becomes expensive. Furthermore, since the permanent magnets 155 and 156 are formed as the ring shape by combination of a plurality of arc-shaped permanent magnets, manufacturing process of the ring shaped permanent magnets 155 and 156 becomes complicated, and the cost of them in manufacturing becomes expensive. As a result, the costs of the actuator using the conventional permanent magnets and coil and the power toothbrush using the same become expensive. Still furthermore, since the permanent magnets 155 and 156 are larger, it is difficult to realize the miniaturization and weight saving of the actuator 150 and the power toothbrush using the same.